Answer
Initial amount $a=8$
Rate of decay $r=15\%$
At $t=3,y=4.9$
Work Step by Step
The given expression is
$\Rightarrow y=8(1-0.15)^t$
The standard form of an exponential decay function is
$y=a(1-r)^t$
Initial amount $a=8$
Rate of decay $r=0.15=15\%$
Substitute $3$ for $t$.
$\Rightarrow y=8(1-0.15)^3$
Simplify.
$\Rightarrow y=8(0.85)^3$
Evaluate the power.
$\Rightarrow y=8(0.614125)$
Simplify.
$\Rightarrow y=4.913$
Round to the nearest tenth.
$\Rightarrow y=4.9$.
